A solar array to power satellite vehicles which is stowable in a small volume for shipment and launch, and that is deployable when aloft to expose a large surface area of solar collectors.
Deployable solar arrays are typically contained in a small envelope when their space vehicle is launched. They are later deployed to an extended configuration to expose areas of solar collectors. Examples of such arrays are shown in the following United States patents:
Avilov U.S. Pat. No. 3,460,992
Harvey et al U.S. Pat. No. 5,296,044
Everman et al U.S. Pat. No. 5,487,791
A review of these patents will disclose remarkable efforts to reduce the weight and increase the reliability of these arrays. Cost, while important, has been and still is subordinate to reliability. The failure of an array to deploy and to survive for its full design life can result in loss of value of the entire craft and its payload. The cost of the craft and its payload is many times that of the array, especially when the payload is unique and employed for very advanced applications.
Because of this, and because of the relatively small number of vehicles involved, the design and manufacture of solar panels and their supporting structure has tended toward the complex, familiar, and costly. They have been carefully and slowly built, almost in a xe2x80x9chandicraftxe2x80x9d sense.
However, with the advent of space-based communication systems, the market for satellites has greatly enlarged. The cost of the payloads, while still considerable, has decreased. Expenses which are tolerable for a few very high value vehicles become unacceptable when the production count will run into the hundreds.
The demand for such a large number of arrays threatens to outstrip the capacity of existing manufacturing plants that were sufficient for the previous slow-paced demand. Multiplying plant capacity can permit faster production schedules, provided that additional skilled personnel can be found, and provided that the additional capital is available. Still the arrays would remain at least as costly.
Also, the problems of producibility remain. Existing constructions are built very painstakingly, because if one part is imperfectly produced, a large part of the entire array often must be scrapped or reworked at considerable cost. This risk and the unfavorable consequences which inevitably occur, has reduced the yield of these arrays.
It is the primary object of this invention to provide a solar panel which can be efficiently manufactured to high standards, and should some part of it be unsuitable, can be quickly and easily repaired or replaced. Thus the entire assembly need no longer be hostage to the acceptability of every part. Instead, all parts will be individually and readily replaceable.
The key subassembly which has the greatest vulnerability during integration and test, the highest value, and the longest repair time is the solar cell stringing. This invention proposes to separate the field of solar cells, traditionally arrayed on blanket systems, into separate but identical modules termed SPMs (solar power modules). This will allow mass production at low cost and availability for change out during test as required. Rapid integration is achieved by integrating each SPM into the xe2x80x9cblanketxe2x80x9d with quick attachment using a minimum number of fastening elements as described herein. The SPMs are hung onto parallel straps of thin (flexible to bending) xe2x80x9cspinesxe2x80x9d spaced to overlay the outside edges of the SPMs. The flexible spines carry all the individual SPMs. The rows of SPMs can be folded to unfold or stow the blanket as an accordion by utilizing the flexibility of the spine straps.
With this invention, it appears likely that an array which formerly required a few months to build, can be built in a day.
However, manufacturing problems are not the only ones solved by this invention. In order to build a truly lightweight structure, the materials of construction must themselves be lightweight, and will often lack much structural strength while in a gravitational field, or in the fields of force that exist at launch or in transporting it to the site where it will be installed. To overcome this, conventional arrays simply provided more strength with more structure, and more cost.
These arrays must be stored in such a way that they can be handled on the ground without extreme care, and which will protect the array from the large launching forces. Then, when the craft is in orbit, the delicate solar blanket must controllably be deployed from the craft and be fully protected during extension to the deployed configuration. This still does not exhaust the problems of most existing arrays. Their tendency is to deploy the structure and lock it physically into a rigid structure. While there are no substantial acceleration forces on it while in orbit, a solar array can be subject to substantial internal forces, for example those which occur during the time while the craft leaves the shadow of the earth and comes into the sunlight. All too often, the different local expansions of material result in a physical snap as relative dimensions of the various parts change with rapidly changing temperature. Such forces can be damaging to the delicate parts of an array, and are a particular nuisance to proper orientation control of the spacecraft. The guide bending or xe2x80x9csnappingxe2x80x9d of this deployed structure causes a shift of mass centers and the spacecraft oscillates about the intended orientation until the xe2x80x9csnapxe2x80x9d has been damped out.
In the course of simplifying the array of this invention, the applicants have taken a different approach to cause and to assure deployment, which eliminates risk of the snapping action which is experienced in much of the prior art.
The consequence of these improvements is to increase the productivity and yield of solar arrays while still providing excellent reliability, at a significantly lower cost.
A solar array according to this invention includes a solar blanket which is folded into adjacent panels that are hinged together in an accordion-folded mode at parallel hinges. A pair of foldable spines is fixed to the panels and runs the length of the array. The hinges are included in the spine. The spines are mounted at one end to a base plate, and also at the other end to a tip plate. The base plate is intended to be attached to the spacecraft structure with a yoke which will provide required standoff for rotational clearance during sun-tracking.
A pantograph deployment structure extends between the two plates. It can be retracted for storage and extended to deploy the blanket. A conductive harness is attached to the blanket to collect current from the panels.
According to a preferred but optional feature of the invention, the deployable structure lies in a plane parallel to the blanket. It includes a plurality of scissor links, and adjacent to each of the plates, a synchronizing link which compels the scissor arms to deploy in the correct direction.
According to another preferred but optional feature of the invention, tensioning springs are contained in at least some of the scissor arms, which tension a cable that tends to pull intersections of opposite scissor links toward one another, thereby to deploy the structure. Deployment is resisted by a lanyard which extends between the plates. When released, the rate at which the tip plate can separate from the base plate and deploy the blanket is limited by limiting the rate of release of lanyard from a damper. Advantageously the lanyard can pass through eyelets on the blanket panels to hold the blanket in its proper position relative to the deployment structure.
According to yet another preferred but optional feature of the invention a kicker spring may be placed at the intersections of the scissor linkages, biasing them toward the deploying direction without imparting shear forces and hence without adding drag.
According to still another preferred but optional feature of the invention, a plurality of tie-down rods are fixed to the base panel and pass through the tip panel. A releasable fastener holds the stored, accordion-folded, blanket until deployment is desired. Release of the fastener enables the array to deploy at a rate limited by the damper.
The above and other features of this invention will be fully understood from the following detailed description and the accompanying drawings, in which: